1. Field of the Invention
The present invention relates to a paper container for fluid substances, and an inside lid used therefor.
2. Description of the Related Art
It is necessary that a container for accommodating fluid substances which are relatively heavy-weight and have the property of oxidizing or evaporating, should possess satisfactory strength, seeping-preventing efficiency, gas-shutoff efficiency and the like. Printing ink represented by, for example, letterpress ink, intaglio plate ink and planographic ink is a high viscosity substance containing volatile matters, in which pigments, lakes and dyes are kneaded into a vehicle. Thus, conventionally, a container therefor has been used in which a trunk member, a bottom member and a lid member are generally formed of metal plates such as a tin plate and steel plate and are manufactured as a can by plate drawing. Although this structure ensures sufficient strength, its heavy weight results in an increase in the transportation costs of containers. In addition, there exist drawbacks in that, since the sealing efficiency of joints of the container is insufficient, infiltration of air may cause the contents of the container to be oxidatively polymerized to be hardened. Further, there also exist drawbacks in that, since this type of container is not combustible and the contents adhere to the container even after use of the container, it is difficult to dispose of the used container and the cost for disposing of the same may increase exceedingly.
For this reason, a jointless container formed by deep-drawing a metal plate has also been used. However, in this type of container as well, there exist drawbacks in that the container is heavy-weight and the cost of manufacturing the same is very high, and that the used containers occupy a large amount of space and are not easy to be disposed of.
Further, fluid substances such as oxidatively-polymerizing printing ink represented by offset ink, polymerizing paints and a reactively-hardening adhesive agent (particularly, offset ink) have high viscosity and are difficult to neatly and quickly be taken out from a container. For this reason, these fluid substances have been often used after their viscosity is lowered by letting them together with the containers into an oven and then heating the contents in advance so that the contents can easily be taken out from the containers. However, heating by using an oven requires a considerable time until the contents entirely get warm. In addition, since it is difficult to heat the contents uniformly, there exists a drawback in that, the fluid substance at a portion near a heat source is excessively heated and an undesirable phenomenon such as skinning may appear. Therefore, there has also been a demand for a container which overcomes this drawback and for which a preferable heating process can be utilized.